Among photodetectors, there are known types in which current signals, generated by photodiodes according to incident light amounts, are logarithmically compressed and output as voltage signals (see, for example, Patent Document 1 and Patent Document 2). This type of photodetector has a merit of being wide in the dynamic range of incident light amount detection.    Patent Document 1: Japanese Published Unexamined Patent Application No. Hei 11-155105    Patent Document 2: Japanese Published Unexamined Patent Application No. Hei 5-219443
However, a photodetector that employs such a logarithmic compression method has a problem that the logarithm compression characteristics (that is, the incident light amount detection characteristics) vary largely with temperature.
The present invention has been made to resolve the above problem and an object thereof is to provide a photodetector with a wide dynamic range of incident light amount detection and a small temperature dependence.